The present disclosure relates generally to variable valve timing for internal combustion engines and, more specifically, to systems and methods for cam phasing control.
Internal combustion engines include a plurality of cylinders with pistons received therein that are connected to drive a crank shaft. Each cylinder has two or more valves that control the flow of air into the cylinder and the flow of exhaust gases out of the cylinder. The intake and exhaust valves can be actuated at different times during the engine cycle (e.g., during the intake and exhaust strokes, respectively) by a cam shaft, which is mechanically connected to be rotated by the crank shaft.
It has been recognized that optimum engine performance (e.g., engine efficiency and emissions) can be obtained if the valve timing varies, for example, as a function of engine speed, engine load, atmospheric pressure, and other factors. During engine operation, a cam phase actuator (cam phaser) can be used to alter a rotational relationship of the cam shaft relative to the crank shaft (i.e., cam phasing), which, in turn, alters when the intake and/or exhaust valves open and close.
Currently, cam phasers can be hydraulically actuated, electronically actuated, or mechanically actuated. For hydraulically actuated cam phasers, there are two operational modes for cam phasing, namely, cam torque actuation mode and oil pressure actuation mode. Cam torque actuation mode utilizes torque pulses imposed on the cam shaft to rotate the cam phaser. Oil pressure actuated mode uses oil pressure from the engine's pump to rotate the cam phaser.